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US scientists have rather disturbingly provided ammunition for shower-dodging geeks to defend their malodorous ways: showers can actually be bad for your health.

According to researchers at the University of Colorado at Boulder, pathogens which occur naturally at low levels in water supplies can accumulate in high concentrations in "biofilms" inside shower heads, meaning that every time you turn on the water, you're getting a faceful of nastiness.

Specifically, the scientists pinpointed Mycobacterium avium - "a pathogen linked to pulmonary disease that most often infects people with compromised immune systems but which can occasionally infect healthy people", according to lead boffin professor Norman Pace.

The team probed 50 shower heads from nine cities in seven states, including Chicago, Denver and New York City. In 30 per cent of them they found "significant levels" of Mycobacterium avium and related pathogens - specifically, "more than 100 times the background levels of municipal water".

Pace said: "There have been some precedents for concern regarding pathogens and showerheads. But until this study we did not know just how much concern."

He warned: "If you are getting a face full of water when you first turn your shower on, that means you are probably getting a particularly high load of Mycobacterium avium, which may not be too healthy."

The University of Colorado seems to have an unhealthy interest in Mycobacterium avium. It previously "found massive enrichments of M. avium in 'soap scum' commonly found on vinyl shower curtains and floating above the water surface of warm therapy pools".

In 2006, Pace plunged again into therapy pools, and identified "high levels of M. avium in the indoor pool environment were linked to a pneumonia-like pulmonary condition in pool attendants known as 'lifeguard lung'".

This in turn led Pace and chums to dismantle the US's shower heads, the results of which investigations are found in the 14 September issue of Proceedings of the National Academy of Sciences (abstract here, more background detail here)

Naturally, you're all wondering whether taking a shower is actually dangerous. Pace concluded: "Probably not, if your immune system is not compromised in some way. But it's like anything else - there is a risk associated with it."

The professor suggested using a metal showerhead, since the plastic type are apparently susceptible to biofilm build-up. Consider yourselves advised. ®

Bootnote

Here's how the Colorado Uni boffins sniffed out their prey: "A molecular genetics technique developed by Pace in the 1990s allowed researchers to swab samples directly from the shower heads, isolate DNA, amplify it using the polymerase chain reaction, or PCR, and determine the sequences of genes present in order to pinpoint particular pathogen types."